Lorea Flores

Does it make economic sense to restore rivers for their ecosystem services

Temperate forests managed to maximize sustainable yield of wood products can reduce the availability of dead wood on the forest floor and in adjacent streams, which in turn can impair ecological processes such as retention and transformation of organic matter. Lack of tools to link ecological processes with their effects on human well-being leads forest managers to ignore the cost on other services from terrestrial and aquatic ecosystems. We examine how adding dead wood to restore stream channel complexity affects the provision and value of selected ecosystem services, mainly related to the retention and transformation of matter and cycling of nutrients, as well as to the effects on aquatic biota. Specifically, we evaluated the cost-effectiveness of stream restoration through a comparative analysis of four reach-scale projects in streams flowing through temperate forest and into a drinking water reservoir and two scenarios of active and passive restoration at the basin scale. Results indicate that the lack of dead wood in streams has an important economic cost because of the effects on fish provisioning, opportunities for recreation and tourism, water purification and erosion control. Active reach-scale restoration resulted in a 10- to 100-fold increase in the monetary benefits provided by streams, accounting as much as 1·8 € per metre of restored river length each year. Results of the reach-scale cost-benefit analyses estimated that the time required to recover the active restoration investment ranged from 15 to 20 years in low- to middle-order streams. Synthesis and applications. Our study showed that restoration of natural wood loading in streams greatly increases the ecosystem services they provide. The benefits in terms of the analysed services surpass the costs of active restoration over realistic timeframes, whereas this was not the case for passive restoration. Inclusion of other ecosystem services such as conservation of biodiversity might make restoration more economically profitable. Overall, our study provides a decision framework for managing temperate riparian forests in the context of ecological services. Our study showed that restoration of natural wood loading in streams greatly increases the ecosystem services they provide. The benefits in terms of the analysed services surpass the costs of active restoration over realistic timeframes, whereas this was not the case for passive restoration. Inclusion of other ecosystem services such as conservation of biodiversity might make restoration more economically profitable. Overall, our study provides a decision framework for managing temperate riparian forests in the context of ecological services

The use of wooden sticks to assess stream ecosystem functioning: Comparison with leaf breakdown rates

Breakdown of organic matter is a key process in streams and rivers, and thus, it has potential to assess functional impairment of river ecosystems. Because the litter-bag method commonly used to measure leaf breakdown is time consuming and expensive, several authors proposed to measure breakdown of wooden sticks instead. Nevertheless, currently there is little information on the performance of wooden sticks versus that of leaves. We compared the breakdown of tongue depressors made of untreated poplar wood, to that of six common leaf species in two large streams in the Basque Country (northern Spain), one polluted and the other unpolluted. Breakdown rates ranged from 0.0011 to 0.0120 day(-1), and were significantly lower in the polluted stream. Wooden sticks performed very similarly to leaves, but were less affected by flood-induced physical abrasion. The ranking of the materials according to their breakdown rate was consistent, irrespective of the stream. The experiments with leaves were 10 times more costly for breakdown rate, 4 times if we include the rest of the variables measured. Therefore wooden sticks offer a promising tool to assess river ecosystem functioning, although more research is necessary to define the thresholds for ecosystem functional impairment.

Compensatory Feeding of a Stream Detritivore Alleviates the Effects of Poor Food Quality when Enough Food is Supplied

Abstract: Availability and quality of food resources limit consumer performance and modulate food webs, which in turn, can affect ecosystem functioning. Availability and quality of food resources can be especially important in streams, where consumers depend on allochthonous organic matter whose availability and quality can differ markedly both spatially and throughout the year. Most studies of the relationships between food quality and detritivore performance have been based on standardized food types and have not been designed to allow consideration of interactions between resource quantity and quality. Our goal was to evaluate the effects of quality and quantity of resource on shredder performance. We raised larvae of the caddisfly Sericostoma vitattum in the laboratory with food taken from a stream reach. We controlled food type (conditioned Alnus glutinosa leaves, natural leaf packs from riffles, and deposits within thick debris jams) and quantity (low: 2 mg individual-1 d-1; high: 10 mg individual-1 d-1). Consumption rate tended to be higher for lower- than for higher-quality materials, and the differences were more marked at high resource quantity. However, this compensatory mechanism was not enough to compensate growth in the case of lowest-quality food. In addition, food quality and quantity interacted to determine the energy allocation to body condition or growth. Our results show that the interaction between resource quality and quantity can influence invertebrate condition and life cycles. Stored organic matter in large jams, despite their poor quality, could enable consumers to survive until the next high-input season.

Restoration of wood loading has mixed effects on water, nutrient, and leaf retention in Basque mountain streams

Dead wood is an important component of natural stream ecosystems, but its abundance has been reduced by human actions. Therefore, in many stream restoration projects dead wood is introduced into stream channels to improve physical habitat, biological communities, and ecosystem functioning. We added dead wood to 4 northern Iberian headwater streams, ranging in mean discharge from 0.026 to 2.5 m3/s, to enhance retention of nutrients, sediments, and organic matter. We placed logs and branches in the stream channels to simulate the amount and orientation found in natural streams and assessed the effects of restoration following a Before-After–Control-Impact design. We measured water and nutrient retention by experimental additions of PO43– and NH4+, with NaCl as a hydrological tracer, and leaf retention by releasing Ginkgo biloba leaves. Introduction of large wood significantly reduced water velocity, especially during high-flow periods, but the overall effects on average nutrient travel distance were not significant. When analyzed individually by stream, effects were significant only for PO43– in 1 stream. Wood addition increased average leaf-litter travel distance overall, but when analyzed individually by stream had no effect in the 2 smaller streams despite the fact that previously reported measures of benthic organic matter increased many fold. This discrepancy between ginkgo measurements and benthic storage raises concerns about the relevance of short-term release measurements and suggests that the effects of wood introduction on nutrient retention might also be stronger than reported here. Overall, wood addition decreased water velocity at all sites, but effects on retention of nutrients and organic matter were variable among sites. Nevertheless, the fact that all statistically significant differences found showed enhanced retention, which can be the basis of important ecosystem services, suggests that wood restoration produces functional benefits beyond the improvement of stream habitat.

Habitat Complexity in Aquatic Microcosms Affects Processes Driven by Detritivores.

Habitat complexity can influence predation rates (e.g. by providing refuge) but other ecosystem processes and species interactions might also be modulated by the properties of habitat structure. Here, we focussed on how complexity of artificial habitat (plastic plants), in microcosms, influenced short-term processes driven by three aquatic detritivores. The effects of habitat complexity on leaf decomposition, production of fine organic matter and pH levels were explored by measuring complexity in three ways: 1. as the presence vs. absence of habitat structure; 2. as the amount of structure (3 or 4.5 g of plastic plants); and 3. as the spatial configuration of structures (measured as fractal dimension). The experiment also addressed potential interactions among the consumers by running all possible species combinations. In the experimental microcosms, habitat complexity influenced how species performed, especially when comparing structure present vs. structure absent. Treatments with structure showed higher fine particulate matter production and lower pH compared to treatments without structures and this was probably due to higher digestion and respiration when structures were present. When we explored the effects of the different complexity levels, we found that the amount of structure added explained more than the fractal dimension of the structures. We give a detailed overview of the experimental design, statistical models and R codes, because our statistical analysis can be applied to other study systems (and disciplines such as restoration ecology). We further make suggestions of how to optimise statistical power when artificially assembling, and analysing, ‘habitat complexity’ by not confounding complexity with the amount of structure added. In summary, this study highlights the importance of habitat complexity for energy flow and the maintenance of ecosystem processes in aquatic ecosystems.